Power MOSFET

In 1969, Hitachi introduced the first vertical power MOSFET, launching a revolution in power electronics that would eventually displace the bipolar transistor from most switching applications. The standard MOSFET, invented at Bell Labs in 1959, was designed for low-power signal processing in integrated circuits. Power applications—motor control, power supplies, audio amplifiers—demanded transistors that could handle high voltages and currents while switching efficiently. The power MOSFET solved this with a vertical structure that allowed current to flow through the bulk of the silicon rather than just along its surface.

The adjacent possible for power MOSFETs required understanding how to build MOSFET structures that could handle kilowatts rather than milliwatts. The original lateral MOSFET design limited current flow to a thin channel at the silicon surface—adequate for logic circuits but fundamentally limited for power applications. The breakthrough was vertical geometry: by directing current flow perpendicular to the chip surface through a thick drift region, designers could achieve both high voltage blocking and high current capacity.

Two competing vertical structures emerged nearly simultaneously. The VMOS (V-groove MOSFET) used a V-shaped channel etched into the silicon. The DMOS (double-diffused MOSFET) used diffusion to create the channel structure. In 1969, Toshihiro Sekigawa and colleagues at Japan's Electrotechnical Laboratory demonstrated the first DMOS with self-aligned gate. T.J. Rodgers at Stanford filed a VMOS patent in 1973. Siliconix commercialized the VMOS in 1975.

The Japanese consumer electronics industry drove early adoption. In 1974, Jun-ichi Nishizawa at Tohoku University developed a power MOSFET specifically for audio amplifiers, and Yamaha immediately licensed it for high-fidelity audio. JVC, Pioneer, Sony, and Toshiba followed within months. The power MOSFET's fast switching speed and immunity to thermal runaway (unlike bipolar transistors) made it ideal for audio applications.

The crucial commercial breakthrough came in 1977-1978. John Moll's team at HP Labs demonstrated that DMOS achieved lower on-resistance and higher breakdown voltage than VMOS. At Stanford, Alex Lidow and Tom Herman invented the HexFET—using hexagonal cell geometry to maximize channel width per unit area. International Rectifier commercialized the HexFET in 1978, and the hexagonal structure became the industry standard (International Rectifier trademarked 'HEXFET' for their product line).

The convergent development across Japan, the United States, and Europe reflected universal demand for efficient power switching. The MOSFET's voltage-controlled switching consumed minimal drive power, unlike current-hungry bipolar transistors. This efficiency advantage proved decisive as switching power supplies and motor drives became ubiquitous.

By 2025, power MOSFETs are everywhere: in every switching power supply, every motor controller, every DC-DC converter. Electric vehicles use thousands of power MOSFETs (or their evolutionary descendants, IGBTs and wide-bandgap devices). The efficiency gains from solid-state power switching—compared to earlier technologies—have saved billions of kilowatt-hours of electricity. The humble power MOSFET, enabling precise electronic control of electrical power, became one of the enabling technologies of the modern energy-efficient world.